The fact that the phenotypic variance is approximately equal among affected individuals in the CC011/Unc strain and among N2 progeny homozygous for the CC011/Unc allele at Ccc1, Ccc2 and Ccc3 at first led us to assume that non-genetic factors were in part responsible for the variance in severity of the colitis phenotype in the CC011/Unc strain and in the backcrosses. The gene discussed is SLC12A2; the disease is colitis.